The invention relates to a method for manufacturing dynamoelectric machines and more particularly relates to a method for protecting the stator windings of such a machine from damage due to having metal fragments lodged therein during a manufacturing process in which metal shavings or chips are cut from portions of the machine housing.
It was common practice before the present invention to perform various machining operations on the housings of dynamoelectric machines during the course of their manufacture in order to appropriately size the machine housing and to provide rabbetted surfaces cut to appropriate tolerances. Characteristically, such machining operations are performed on the housing after a stator and stator winding are assembled in the housing. Inevitably such machining operations result in a large number of metal chips and shavings being lodged in and around the stator windings of the machines. If those metal fragments were allowed to remain in the windings, they could result in various forms of failure of the machine when it is placed in operation. For example, the metal fragments could work down into the winding insulation and eventually cut it to cause an electrical short circuit between the winding coils, or to cause an electrical grounding failure in the machine. Alternatively, the metal fragments might work their way into the machine air gap and cause a breakdown of insulation that could completely burn out the rotor or stator windings.
In the past, such undesirable consequences were successfully avoided by carefully extracting all metal fragments from the stator windings of the machines before they were placed in use. For electric machines having cast iron or steel housings, such removal operations are usually facilitated by applying a magnetic field to the components of the machine sub-assembly to assist a fan or blower means in extracting the loose metal fragments from the windings. However, for machines that utilize non-ferrous metals for the housing, such as machines having aluminum housings, it is necessary to rely on extraction means other than magnetic fields. In fact, practical experience has demonstrated that once aluminum cutting chips become lodged in the stator windings of a dynamoelectric machine it is very time consuming and frequently nearly impossible to extract all of the chips before the machine is placed in use.
This problem is complicated by the fact that high volume production of relatively small dynamoelectric machines of the type commonly employing aluminum housings is normally characterized by sizing and rabbetting operations that utilize high speed cutting rates for these cutting tools. Consequently, the machining operations produce a profusion of metal chips and fragments that are scattered in all directions in and around the stator windings. Attempts to air blow or vacuum these particles from the windings is partially frustrated by the typically curled or sharply angled configurations of the chips and shavings that are cut from the housings during such machining operations. These twisted metal particles become tightly hooked into the interstices of the stator windings and frequently are almost impossible to remove.
In addition to the vacuuming and blowing operations mentioned above that are conventional techniques for attempting to remove machining fragments from the windings of dynamoelectric machines, it is known that some attempts have been made to employ wide rubber bands to at least partially cover the outside diameter of the end turns of stator coils during such machining operations in an attempt to block metal fragments from ever becoming lodged on the outer surfaces of the windings. However, that technique has been only partially successful in attaining the desirable objective of preventing metal fragments from being lodged in the windings. As mentioned above, the high rates of cutting used in performing many machining operations on aluminum motor housings results in metal chips and shavings being thrown in large volume in many directions over the housings and inevitably some of these chips enter the internal area of even such partially shielded stator windings, so the chips become lodged and difficult or impossible to remove without damaging the windings.
In addition to their inability to completely protect the stator windings from metal fragments developed by the machining operations normally performed on a stator housing after a stator is mounted in it, the wide rubber band used in prior art techniques to partially cover the exterior surface of the stator windings were found objectionable due to the need to custom fabricate different sizes of rubber bands for various different sizes of stator end turns that are inevitably encountered in manufacturing a range of ratings of dynamoelectric machines. Thus, it would be desirable to not only provide a means for effectively isolating the stator windings of dynamoelectric machines from metal fragments machined off of the stator housings of the machines during their manufacture, but it would be desirable to provide such means in a form that could readily accommodate a large number of different lengths of stator end turns so that it would not be necessary to either custom make a number of different shielding means or to custom install shielding means carefully over each end turn arrangement of the stator windings of given machines.